A8 Goldschmidt Conference Abstracts 2007

Evolution of upper mantle in Geology, mineralogy, and genesis of Southern Sanandaj – Sirjan zone of the Iwami-Ginzan silver mine, Japan

Iran M. AKASAKA, H. KOMURO AND H. OHIRA H. AHMADIPOUR Department of Geoscience, Shimane University, Matue, Japan ([email protected]; komuro @riko.shimane- Dept. of Geology,Shahid Bahonar University, Kerman, Iran u.ac.jp; [email protected]) ([email protected])

The Iwami-ginzan silver mine produced an enormous In the Southern Sanandaj – Sirjan zone (Iran), there are amount of silver following its discovery in 1309, and thus several ultramafic complexes such as Kuhshah, Soghan and played a very important role as a major silver producing field, Abdasht. They have many evidences for belonging to the not only in Japan, but also at a global scale. The Iwami-ginzan upper mantle and contain dunite, harzburgite and chromitite silver deposit contains two types of ore bodies named the that in some parts, have been invaded by pyroxenitic Fukuishi and Eikyu deposits: the former is disseminated type, intrusions.They show some evidences in various scales for and the latter vein-type. They are related to the dacite intrusion evolution of upper mantle in this part of Iran.In the field, there generated during the Pleistocene epoch of the Quaternary are many pyroxenite veins and dykes that have been cut (Sakota et al. 2000). ultramafic sections and implies that upper mantle in this area The ore minerals of the Eikyu deposit are native silver, have partially melted and then, resulting melts, have argentite, electrum, matildite, polybasite, stromeyerite, silver- perculated in the other parts of the complexes and impregnated bearing tetrahedrite, aikinite, Bi-bearing polybasite, them. In microscopic scale, existence of second generation of wittichenite, tetrahedrite-tennantite, enargite, chalcopyrite, orthopyroxene, clinopyroxene, olivine and euhedral chalcocite, galena, sphalerite, and pyrite. The genetic chromespinels indicate strong perculation and melt/rock temperature may be about 200°C. The disseminated Fukuishi interaction in the upper mantle of the area. First generation deposit contained not only native silver, argentite and hematite minerals are large elongated and deform grains, while second but also jalpaite, mackinstryite, pearceite stromeyerite, and ones have crystallized as small interstitial grains without any , chlorargyrite. The genetic temperature of the Fukuishi deposit deformation. From mineral chemistry point of view, there are might be about 100°C. also two generation of minerals with different chemical There is a significant gravity anomaly in the Iwami-ginzan composition. For example, first generation orthopyroxenes area, indicating existence of a cauldron, and the Iwami-ginzan (opx1) rich in compatible and depleted in incompatible is situated at the rim of the cauldron. During the Neogene, elements relative to second generation ones, (NiO in hydrothermal solutions are considered to have repeatedly Opx1=0.16 w% and NiO in Opx2=0.07 w%). In infiltrated the faults and fractures in and around the cauldron. clinopyroxenes and olivines, there are similar properties too. The hydrothermal solutions which produced the Iwami-ginzan Geochemical data on whole rocks indicate harzburgites are silver mine also passed through these pre-existing faults and depleted mantle rocks that have partially melted and then fractures. The very high ore grades in the Iwami-ginzan silver invaded and impregnated by silicate ascending melts. REE mine may have been caused by remobilization of earlier patterns of these harzburgites show depletion relative to mineralization, and hence are the product of multiple episodes primitive mantle, but LREE enrichments relative to MREE are of ore genesis. evident. This feature can be produced by entrance of more incompatible REE(LREE) from melts to the harzburgites. References All of these evidenses indicate upper mantle in Sanandaj- Sakota, M., Kodama, T. and Inoue, T. (2000) Shigen-chisitu, Sirjan zone, have been affected by partial melting and 50, 45-60. melt/rock interaction. So there is strong heterogenity in various scales in this part. The ultramafic complexes of Sanandaj-Sirjan have ascent and empleced in the crust tectonically, and textural features show reequilibriation in crustal conditions .

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